The broad, long-term objective of the research is to obtain the structure of mammalian (rat) ribosomes and to derive from the structure a coherent molecular account of the function of the particle in protein synthesis. A requisite for the resolution of the structure is the sequences of nucleotides and of amino acids in the constituent nucleic acids and proteins. These sequences are necessary but hardly likely to be sufficient to solve the structure, just as knowledge of the structure is unlikely to lead parri passu to an understanding of the function of ribosomes. However, it is difficult to imagine being able to decipher the structure without the chemistry of the constituents or to describe function without knowledge of the structure. The chemistry may also help in understanding the evolution of ribosomes, in defining the rules that govern the interaction of the proteins and the rRNAs, and in uncovering the amino acid sequences that direct the proteins to the nucleolus for assembly on nascent rRNA. A commitment has been made both to the acquisition of the chemical data and to the solution of the structure. The specific aims are: (1) To continue the determination of the sequences of amino acids in rat ribosomal proteins by a combination of protein chemistry and recombinant DNA technology. (2) To relate the structure of rat ribosomal proteins to their function by a combination of molecular genetic and biochemical techniques using yeast to further the aim.